System and Process for Producing Nanowire Composites and Electronic Substrates Therefrom

ABSTRACT

The present invention relates to a system and process for producing a nanowire-material composite. A substrate having nanowires attached to a portion of at least one surface is provided. A material is deposited over the portion to form the nanowire-material composite. The process further optionally includes separating the nanowire-material composite from the substrate to form a freestanding nanowire-material composite. The freestanding nanowire material composite is optionally further processed into a electronic substrate. A variety of electronic substrates can be produced using the methods described herein. For example, a multi-color light-emitting diode can be produced from multiple, stacked layers of nanowire-material composites, each composite layer emitting light at a different wavelength.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/274,904, filed Nov. 20, 2008, which is a divisional of U.S. patentapplication Ser. No. 11/225,951, filed Sep. 14, 2005, now U.S. Pat. No.7,468,315 which is a divisional of U.S. patent application Ser. No.10/910,800, filed Aug. 4, 2004, now U.S. Pat. No. 7,091,120, whichclaims the benefit of U.S. Provisional Patent Application No.60/491,979, filed Aug. 4, 2003, each of which is incorporated herein inits entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to semiconductor devices, and moreparticularly, to the preparation of active elements for use insemiconductor devices.

2. Related Art

An interest exists in industry in developing low cost electronics, andin particular, in developing low cost, large area electronic devices.Availability of such large area electronic devices could revolutionize avariety of technology areas, ranging from civil to militaryapplications. Example applications for such devices include drivingcircuitry for active matrix liquid crystal displays (LCDs) and othertypes of matrix displays, smart libraries, credit cards, radio-frequencyidentification tags for smart price and inventory tags, securityscreening/surveillance or highway traffic monitoring systems, large areasensor arrays, and the like.

Current approaches involve using amorphous silicon or organicsemiconductors as the base materials for electronic devices, such asthin-film transistors (TFTs). However, amorphous silicon and organicsemiconductors have performance limitations. For example, they exhibitlow carrier mobility, typically about 1 cm²/V_s (centimeter squared pervolt second) or less. Furthermore, they require relatively expensiveprocesses, such as laser induced annealing, to improve theirperformance.

An alternative approach involves using semiconductor nanowires as thebuilding blocks for large area electronic and optoelectronic devices. Awide range of Group IV, III-V and II-VI semiconductor nanowires can berationally synthesized with tunable chemical composition, physicaldimension and electronic properties, see Duan, X., et al. NanowireNanoelectronics Assembled from the Bottom-up, in MolecularNanoelectronics, Reed, M. ed., American Scientific Publisher, New York(2002); Duan, X. and Lieber, C. M., Adv. Mater. 12:298-302 (2000) andGudiksen, M. S., et al. J. Phys. Chem. B 105:4062-4062 (2001), each ofwhich are incorporated herein, in their entirety, for all purposes.

The extended longitudinal dimension and reduced lateral dimension makesnanowires the smallest dimension materials for efficient transport ofelectrical carriers. A variety of nanodevices have been demonstratedusing the nanowires, including field effect transistors (FETs), logiccircuits, memory arrays, light-emitting diodes (LEDs) and sensors, seeHuang, Y. et al., Nano Letters 2:101-104 (2002); Huang, Y. et al.,Science 294:1313-1317 (2001); Duan, X., et al., Nano Letters 2:487-490(2002); Wang, J., et al., Science 293:1455-1457 (2001); Cui, Y., et al.,Science 293:1289-1292 (2001); U.S. Pat. No. 7,067,867, which isincorporated herein, in its entirety, for all purposes.

While nanowires show promise as high mobility electrical carriers, theiruse in devices is currently limited by difficulties that arise inharvesting nanowires from the substrates on which they have beensynthesized. If the nanowires are not harvested, then the range ofnanodevices that employ nanowires are limited because only thosesubstrates suitable for nanowire synthesis can be used in the device.Currently, nanowires are harvested by separating the nanowires from thesubstrate using mechanical devices, such as a razor blade or otherknife-edges. This method has drawbacks including possible physicaldamage to the nanowires during harvesting. Therefore, there is a need todevelop efficient methods of harvesting nanowires from the substrates onwhich they are synthesized.

SUMMARY OF THE INVENTION

In a first aspect, the present invention relates to a system and processfor producing a nanowire-material composite. A substrate is providedhaving nanowires attached to a portion of at least one surface. Amaterial is deposited over the portion to form the nanowire-materialcomposite. The nanowire-material composite is optionally separated fromthe substrate to form a freestanding nanowire-material composite.

In another aspect, the present invention relates to a system and processfor depositing oriented nanowires. A first substrate having nanowiresattached to a portion of at least one surface is provided. Each nanowirehas a first end attached to the portion. A material is deposited overthe portion to form a nanowire-material composite. The nanowire-materialcomposite is patterned to form a patterned composite. The patternedcomposite is separated from the first substrate. The patterned compositeis applied to a second substrate such that the nanowires are alignedsubstantially parallel to the second substrate. The material isoptionally removed from the nanowire-material composite to form on thesecond substrate a thin film of nanowires aligned substantially parallelto the second substrate and having a sufficient density to achieve anoperational current level. A plurality of semiconductor device regionsis defined in the thin film of nanowires. Contacts are formed at thesemiconductor device regions to thereby provide electrical connectivityto the plurality of semiconductor devices.

In another aspect, the invention relates to a system and process forproducing an electronic substrate. A nanowire-material compositecomprising a plurality of nanowires is attached to a portion of asubstrate. The nanowire-material composite is patterned to define one ormore semiconductor device regions. Contacts are formed at thesemiconductor device regions to thereby provide electrical connectivityto the device regions. A nanowire-material composite can be attached tothe portion of the substrate by lamination. The nanowire-materialcomposite is optionally planarized to expose a portion of the nanowiresafter the composite is attached to the substrate. A dielectric layer isoptionally deposited on the nanowire-material composite. The dielectriclayer is etched to form a patterned dielectric layer and to expose aportion of the nanowire-material composite to define the one or moresemiconductor device regions. The exposed nanowire-material composite isoptionally doped. The dielectric layer is removed. The semiconductordevice regions are metallized to form electrical connectivity to thedevice regions.

A p-n junction is optionally formed in the nanowire-material composite.The nanowires are formed from at least one light emitting semiconductingmaterial such that the p-n junctions emit light during operation. Thelight emitting materials include at least one of GaN, GaP, GaAs, InP,InAs, ZnO and a combination thereof. Alternatively, thenanowire-material composite is formed from a plurality ofnanowire-material composite layers. Each nanowire-material compositelayer includes at least one of the light-emitting semiconductingmaterials selected to emit light at a wavelength different from theother layers.

In an aspect, a first nanowire-material composite layer of the pluralityof nanowire-material composite layers is formed from at least one lightemitting semiconducting material selected to emit light at a blue lightwavelength. A second nanowire-material composite layer of the pluralityof nanowire-material composite layers is formed from at least onelight-emitting semiconducting material selected to emit light at a greenlight wavelength. A third nanowire-material composite layer of theplurality of nanowire-material composite layers from at least onelight-emitting semiconducting material selected to emit light at a redlight wavelength. The first nanowire-material composite layer is coupledto a first surface of the second nanowire-material composite layer. Asecond surface of the second nanowire-material composite layer iscoupled to a first surface of the third nanowire-material compositelayer. A second surface of the third nanowire-material composite layeris attached to the substrate.

In another aspect, the present invention relates to a system and processfor forming a composite. A plurality of nanowires are grown on a portionof a substrate, each nanowire having an end attached to the portion. Amaterial is deposited on the substrate to cover the portion. Thematerial encases the plurality of nanowires on the portion to form ananowire-material composite layer. A material applicator is optional,which deposits the material on the substrate. The plurality of nanowiresare optionally substantially aligned parallel to their long axis in thematerial. The material applicator flows the material onto the substrateto align the plurality of nanowires. A composite hardener is optional,which hardens the material on the portion. A composite processor isoptional. A separator is optional, which separates the nanowire-materialcomposite from the substrate.

In another aspect, the present invention relates to a process forproducing a nanowire-material composite. The process comprisescontacting nanowires with a material to form a mixture and depositingthe mixture on a substrate to form a nanowire-material composite. Thesubstrate comprises a semiconductor, glass, ceramic, polymer, metal,composite thereof, one or both of the interior and exterior surface of atube or an irregular object, e.g. reticulated macroporous metal, oxideor ceramic.

The process optionally further comprises hardening the composite,separating the composite from the substrate to form a free-standingnanowire-material composite, and aligning the nanowires, such as byapplying an electric field across the composite.

In another aspect, the present invention relates to a process forforming a nanowire array and a nanowire array prepared according to theprocess. The process comprises providing a nanowire-material composite,applying a mask comprising a pattern to the nanowire-material compositeto form a masked composite; removing a portion of the material from thecomposite to expose the nanowires embedded in the portion and form anarray of exposed nanowires in said nanowire-material composite.

The mask can comprise a metal foil comprising a pattern that allows forthe selective removal of material from the composite. The patternscomprise an array of shapes, (e.g. circles, squares, triangles,rectangles and the like). The material is removed using a plasma etch,organic solvent, or other way.

In another aspect, the present invention relates to a process forproducing a high capacitance capacitor, and a capacitor produced by theprocess. The process comprises providing a free-standingnanowire-material composite, depositing a metal on both surfaces of thecomposite film, depositing an insulator on a metal surface to form acapacitor film, and assembling a capacitor. The assembling stepcomprises optional further processing steps including, but not limitedto attaching leads to the metal surfaces, rolling the capacitor film andsealing the film in a canister. The nanowires are optionally oriented inthe nanowire-material composite, such as orienting the nanowiresperpendicular to the composite surface.

In another aspect, the present invention relates to an alternativeprocess for producing a high capacitance capacitor, and a capacitorproduced by the process. The process comprises providing a metal foilhaving a surface coated with an insulator, depositing gold nanoparticleson a portion of the insulator, growing nanowires on the portion,depositing a material over the portion to embed the nanowires and form ananowire-material composite, depositing metal on the nanowire-materialcomposite to form a capacitor film, and assembling the capacitor.

In another aspect, the present invention relates to a process ofproducing a tubular nanowire-material composite. The process comprisescontacting nanowires with a material to form a mixture, and extrudingthe mixture to form a tubular nanowire-material composite. The processoptionally further comprises removing a portion of the material from oneor both of the inner and outer surfaces of the tubular nanowire-materialcomposite to expose a portion of the nanowires.

In another aspect, the present invention relates to an alternativeprocess of producing a tubular nanowire-material composite. The processcomprises providing a substrate having nanowires attached perpendicularto a portion of at least one surface, and depositing a material over theportion to form a nanowire-material composite. The process optionallyfurther comprises hardening the composite by removing solvent orpolymerizing the material. The process further comprises separating thenanowire-material composite from the substrate to form a free-standingnanowire-material composite, optionally cutting the free-standingcomposite into strips, and bonding together the ends of thefree-standing composite to form a tubular nanowire-material composite.The bonding step can comprise gluing together the ends of thefree-standing composite. The process optionally further comprisesremoving a portion of the material from one or both of the inner andouter surfaces of the tubular nanowire-material composite to partiallyexpose the nanowires.

In another aspect, the present invention relates to a freestandingnanowire-material composite. The freestanding nanowire-materialcomposite can be in the form of a sheet that can be rolled and storedfor later use or further processing. The nanowire-material compositeoptionally comprises a portion of exposed nanowires. The exposednanowires are optionally exposed in an array of circular wells.

These and other objects, advantages and features will become readilyapparent in view of the following detailed description of the invention.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the pertinent art to makeand use the invention.

FIG. 1 shows a view of a portion of a thin film of nanowires, accordingto an example embodiment of the present invention.

FIG. 2 shows a semiconductor device that includes a thin film ofnanowires, according to an example embodiment of the present invention.

FIGS. 3A-3E show nanowires doped according to various exampleembodiments of the present invention.

FIGS. 4A and 4B show examples of a semiconductor device, doped accordingto example doping embodiments of the present invention.

FIG. 5 is a flow diagram for a process for producing a freestandingnanowire-material composite, according to an embodiment of the presentinvention.

FIGS. 6A-6C illustrate a freestanding nanowire-material composite beingfabricated on a substrate, according to the process of FIG. 5.

FIG. 7 is a flow diagram for a process for aligning nanowires on asubstrate, according to an embodiment of the present invention.

FIGS. 8A-8F illustrate nanowires being aligned on a substrate accordingto the process of FIG. 7.

FIG. 9 is a flow diagram for a process of producing an electronicsubstrate using nanowires, according to an embodiment of the presentinvention.

FIG. 10 is a flow diagram of optional processing steps in the process ofproducing an electronic substrate using nanowires, according to anembodiment of the present invention.

FIGS. 11A-11B show plan and side views, respectively, of ananowire-material composite attached to a substrate.

FIGS. 12A-12B show plan and side views, respectively, of a planarizednanowire-material composite attached to a substrate.

FIGS. 13A-13B show plan and side views, respectively, of a patternednanowire-material composite attached to a substrate.

FIGS. 14A-14B show plan and side views, respectively, of a dielectriclayer deposited over the patterned nanowire-material composite.

FIGS. 15A-15B show plan and side views, respectively, of a patterneddielectric layer covering a patterned nanowire-material composite andhaving exposed nanowires.

FIGS. 16A-16B show plan and side views, respectively, of a dielectriclayer covering a patterned nanowire-material composite and havingexposed nanowires, after a doping step.

FIGS. 17A-17B show plan and side views, respectively, of a patternednanowire-material composite having areas of doping.

FIGS. 18A-18B show plan and side views, respectively, of an electronicsubstrate having source, gate and drain electrodes metallized on ananowire-material composite.

FIGS. 19A-19E show a nanowire-material composite being processed to forman electronic substrate, according to an embodiment of the presentinvention.

FIG. 20 shows a multilayered light-emitting diode having three layers ofdifferent nanowire-material composites, according to an embodiment ofthe present invention.

FIG. 21 shows an electronic absorption spectrum of various semiconductornanowires and their respective absorption spectrum.

FIG. 22 is a flow diagram of steps in the solution-based process ofproducing a nanowire-material composite, according to an embodiment ofthe present invention.

FIG. 23A is a flow diagram of steps in a process of producing a nanowirearray, according to an embodiment of the present invention.

FIG. 23B shows an exemplary mask that can be used in a process ofproducing a nanowire array, according to an embodiment of the presentinvention.

FIG. 24 is a diagram illustrating a nanowire array, prepared accordingto an embodiment of the present invention.

FIG. 25A is a flow diagram of steps in a process of producing ahigh-capacitance capacitor comprising a nanowire-material composite,according to an embodiment of the present invention.

FIG. 25B shows an exemplary capacitor produced according to anembodiment of the present invention.

FIG. 25C shows an exemplary capacitor produced according to anembodiment of the present invention.

FIG. 26 is a flow diagram of steps in an alternative process ofproducing a high-capacitance capacitor comprising a nanowire-materialcomposite, according to an embodiment of the present invention.

FIG. 27A is a flow diagram of steps in a process of producing flexiblenanofur, according to an embodiment of the present invention.

FIG. 27B shows exemplary nanofur being produced according to anembodiment of the present invention.

FIG. 28A is a flow diagram of steps in a process of producing a tubularnanowire-material composite, according to an embodiment of the presentinvention.

FIG. 28B shows an exemplary tubular nanowire-material composite producedaccording to an embodiment of the present invention.

FIG. 29A is a flow diagram of steps in an alternative process ofproducing a tubular nanowire-material composite, according to anembodiment of the present invention.

FIG. 29B shows an alternative exemplary tubular nanowire-materialcomposite produced according to an embodiment of the present invention.

FIG. 30 is a diagram illustrating a tubular nanowire-material composite,prepared according to an embodiment of the present invention.

FIG. 31 is a Scanning Electron Microscope (SEM) image of ananowire-material composite comprising nanowires oriented perpendicularto the surface of the composite, prepared according to an embodiment ofthe present invention.

FIG. 32 is a SEM image of a nanowire-material composite comprisingrandomly oriented nanowires, prepared according to an embodiment of thepresent invention.

FIG. 33 is a SEM image of a nanowire-material composite comprising aporous material and randomly oriented nanowires, prepared according toan embodiment of the present invention.

FIG. 34 is a SEM image of a nanowire-material composite comprisingrandomly oriented nanowires, prepared according to an embodiment of thepresent invention.

The present invention will now be described with reference to theaccompanying drawings. In the drawings, like reference numbers indicateidentical or functionally similar elements. Additionally, the left-mostdigit(s) of a reference number identifies the drawing in which thereference number first appears.

DETAILED DESCRIPTION OF THE INVENTION Introduction

It should be appreciated that the particular implementations shown anddescribed herein are examples of the invention and are not intended tootherwise limit the scope of the present invention in any way. Indeed,for the sake of brevity, conventional electronics, manufacturing,semiconductor devices, and nanotube and nanowire technologies and otherfunctional aspects of the systems (and components of the individualoperating components of the systems) may not be described in detailherein. Furthermore, for purposes of brevity, the invention isfrequently described herein as pertaining to a semiconductor transistordevice. It should be appreciated that the manufacturing techniquesdescribed herein could be used to create any semiconductor device type,and other electronic component types. Further, the techniques would besuitable for application in electrical systems, optical systems,consumer electronics, industrial electronics, wireless systems, spaceapplications, or any other application.

As used herein, the term nanowire generally refers to any elongatedconductive or semiconductive material that includes at least one crosssectional dimension that is less than 500 nm, and preferably, less than100 nm, and has an aspect ratio (length:width) of greater than 10,preferably, greater than 50, and more preferably, greater than 100.Examples of such nanowires include semiconductor nanowires as describedin Published International Patent Application Nos. WO 02/17362, WO02/48701, and WO 01/03208, each of which is incorporated in its entiretyfor all purposes, carbon nanotubes, and other elongated conductive orsemiconductive structures of like dimensions. Particularly preferrednanowires include semiconductive nanowires, that are comprised ofsemiconductor material selected from, e.g., Si, Ge, Sn, Se, Te, B, C(including diamond), P, B—C, B—P(BP6), B—Si, Si—C, Si—Ge, Si—Sn andGe—Sn, SiC, BN/BP/BAs, AlN/AlP/AlAs/AlSb, GaN/GaP/GaAs/GaSb,InN/InP/InAs/InSb, BN/BP/BAs, AlN/AlP/AlAs/AlSb, GaN/GaP/GaAs/GaSb,InN/InP/InAs/InSb, ZnO/ZnS/ZnSe/ZnTe, CdS/CdSe/CdTe, HgS/HgSe/HgTe,BeS/BeSe/BeTe/MgS/MgSe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbO, PbS,PbSe, PbTe, CuF, CuCl, CuBr, CuI, AgF, AgCl, AgBr, AgI, BeSiN2, CaCN₂,ZnGeP₂, CdSnAs₂, ZnSnSb₂, CuGeP₃, CuSi₂P₃,(Cu,Ag)(Al,Ga,In,Tl,Fe)(S,Se,Te)₂, Si₃N₄, Ge₃N₄, Al₂O₃,(Al,Ga,In)₂(S,Se,Te)₃, Al₂CO, and an appropriate combination of two ormore such semiconductors. In certain aspects, the semiconductor maycomprise a dopant from a group consisting of: a p-type dopant from GroupIII of the periodic table; an n-type dopant from Group V of the periodictable; a p-type dopant selected from a group consisting of: B, Al andIn; an n-type dopant selected from a group consisting of: P, As and Sb;a p-type dopant from Group II of the periodic table; a p-type dopantselected from a group consisting of: Mg, Zn, Cd and Hg; a p-type dopantfrom Group IV of the periodic table; a p-type dopant selected from agroup consisting of: C and Si; or an n-type is selected from a groupconsisting of: Si, Ge, Sn, S, Se and Te.

Hence, although the term nanowire is referred to throughout thedescription herein for illustrative purposes, it is intended that thedescriptions herein also encompass the use of nanotubes. Nanotubes canbe formed in combinations/thin films of nanotubes as is described hereinfor nanowires, alone or in combination with nanowires, to provide theproperties and advantages described herein.

Furthermore, it is noted that thin film of nanowires of the presentinvention can be a heterogeneous film, which incorporates semiconductornanowires and/or nanotubes, and/or nanowires/nanotubes of differentcomposition and/or structural characteristics. For example, aheterogeneous film can include nanowires/nanotubes with varyingdiameters and lengths, and nanotubes and/or nanotubes that areheterostructures having varying characteristics.

In the context of the invention, the substrate to which nanowires areattached may comprise: a uniform substrate, e.g., a wafer of solidmaterial, such as silicon, glass, quartz, polymerics, etc.; a largerigid sheet of solid materials, e.g., glass, quartz, plastics such aspolycarbonate, polystyrene, etc., or can comprise additional elements,e.g., structural, compositional, etc. A flexible substrate, such as aroll of plastic such as polyolefins, polyamide, and others, atransparent substrate, or combinations of these features can beemployed. For example, the substrate may include other circuit orstructural elements that are part of the ultimately desired device.Particular examples of such elements include electrical circuit elementssuch as electrical contacts, other wires or conductive paths, includingnanowires or other nanoscale conducting elements, optical and/oroptoelectrical elements (e.g., lasers, LEDs, etc.), and structuralelements (e.g., microcantilevers, pits, wells, posts, etc.).

The substrates to which nanowires are grown, attached or processed mayfurther comprise irregular surfaces. For example, nanowires may be grownor attached to substrates such as the interior and exterior surfaces ofa tube and interior and exterior surfaces of a porous medium, e.g.reticulated macroporous metals, oxides, ceramics and other porousmedium.

By substantially aligned or oriented is meant that the longitudinal axesof a majority of nanowires in a collection or population of nanowires isoriented within 30 degrees of a single direction. Although the majoritycan be considered to be a number of nanowires greater than 50%, invarious embodiments, 60%, 75%, 80%, 90%, or other percentage ofnanowires can be considered to be a majority that are so oriented. Incertain preferred aspects, the majority of nanowires are oriented within10 degrees of the desired direction. In additional embodiments, themajority of nanowires may be oriented within other numbers or ranges ofdegrees of the desired direction.

It should be understood that the spatial descriptions (e.g., above,below, up, down, top, bottom, etc.) made herein are for purposes ofillustration only, and that devices of the present invention can bespatially arranged in any orientation or manner.

Nanowire Film Embodiments

The present invention is directed to a method of harvesting nanowiresand the use of nanowires in systems and devices to improve system anddevice performance. For example, the present invention is directed tothe use of nanowires in semiconductor devices. According to the presentinvention, multiple nanowires are formed into a high mobility thin filmand/or a nanowire-material composite. The thin film and/or composite ofnanowires is used to harvest nanowires and/or in electronic devices toenhance the performance and manufacturability of the devices.

FIG. 1 shows a close-up view of a thin film of nanowires 100, accordingto an example embodiment of the present invention. Thin film ofsemiconductor nanowires 100 can be used instead of amorphous silicon ororganic thin films in conventional electronic devices to achieveimproved device behavior, while allowing for a straightforward andinexpensive manufacturing process. Through the use of thin films ofnanowires, the present invention is particularly adapted to making highperformance, low cost devices on large and flexible substrates.

Note that thin film of nanowires 100 as described herein may be formedin a wide range of possible surface areas. For example, thin films ofnanowires 100 of the present invention can be formed to have functionalareas greater than 1 mm², greater than 1 cm², greater than 10 cm²,greater than 1 m², and even greater or smaller areas.

As shown in FIG. 1, thin film of nanowires 100 includes a plurality ofindividual nanowires closely located together. Thin film of nanowires100 can have a variety of thickness amounts that are equal to or greaterthan the thickness of a single nanowire. In the example of FIG. 1, thenanowires of thin film of nanowires 100 are aligned such that their longaxes are substantially parallel to each other. Note that in alternativeembodiments, the nanowires of thin film of nanowires 100 are notaligned, and instead can be oriented in different directions withrespect to each other, either randomly or otherwise. In an alternativeembodiment, the nanowires of thin film of nanowires 100 may beisotropically oriented, so that high mobility is provided in alldirections. Note that the nanowires of thin film of nanowires 100 may bealigned in any manner relative to the direction of electron flow inorder to enhance performance as required by a particular application.

FIG. 2 shows a semiconductor device 200 that includes thin film ofnanowires 100, according to an example embodiment of the presentinvention. In FIG. 2, semiconductor device 200 is shown as a transistor,having a source electrode 202, a gate electrode 204, a drain electrode206, formed on a substrate 208. Thin film of nanowires 100 is coupledbetween source electrode 202 and drain electrode 206 over a portion ofgate electrode 204. Alternatively, gate electrode 204 is formed overnanowires 100, which are coupled between source electrode 202 and drainelectrode 206. Thin film of nanowires 100 substantially operates as achannel region for the transistor of semiconductor device 200, andallows semiconductor 200 to operate with enhanced characteristics, asfurther described herein. Numerous substrate types applicable tosubstrate 208 are described elsewhere herein.

Note that semiconductor device 200 is shown as a transistor in FIG. 2for illustrative purposes. It would be understood to persons skilled inthe relevant art(s) from the teachings herein that thin film ofnanowires 100 can be included in semiconductor device types in additionto transistors, including diodes.

In embodiments, the nanowires of thin film of nanowires 100 are singlecrystal semiconductor nanowires that span all the way between sourceelectrode 202 and drain electrode 206. Hence, electric carriers cantransport through the single crystal nanowires, resulting in highmobility that is virtually impossible to obtain with current amorphousand polysilicon technologies.

In addition, and without being bound to any particular theory ofoperation, due to a one-dimensional nature of the electron-wavetraversing inside the nanowire channel, and a reduced scatteringprobability, it may be possible for nanowires to achieve even highermobility than a bulk single crystal material. Nanowires can be designedto be a “ballistic” transport for electrical carries. “Ballistic” isused herein to mean transport through a nanowire with no scattering andwhere the nanowire has quantized resistance.

Note that a variety of contact area types can be formed forsemiconductor devices incorporating nanowires. Contact area is usedherein to mean the electrical connectivity between an electrode andanother element of the device, for example, the connectivity between thegate electrode, a dielectric layer and a nanowire in a MOSFET. Thecontact areas can be Ohmic and non-Ohmic. Alternatively, a non-ohmicSchottky diode barrier contact can be used as an electrode. A Schottkydiode barrier contact is commonly used for a III-V semiconductormaterial when it is difficult to make a high quality gate dielectric.Source electrodes 202, gate electrodes 204, and drain electrodes 206 areformed of a conductive material, such as a metal, alloy, silicide,polysilicon, or the like, including combinations thereof, as would beapparent to a person having ordinary skill in the art.

As described above, the nanowires of thin film of nanowires 100 can bealigned or oriented. For example, the nanowires of thin film ofnanowires 100 shown in FIG. 2 can be aligned parallel to the length ofthe channel between source electrode 202 and drain electrode 206, or canbe aligned in alternative ways.

Thin film of nanowires 100 can be formed with a sufficient number ofnanowires to provide desired characteristics for semiconductor device200. For example, thin film of nanowires 100 can be formed of asufficient number or density of nanowires to achieve a desiredoperational current density or current level desired for the particularapplication. For example, the current level may be in the nanoamp range,including 2 nanoamps, and greater and lesser current levels. Forinstance, in the transistor example of FIG. 2, thin film of nanowires100 can be formed to have a current level in the channel of greater thanabout 10 nanoamps.

For example, to achieve the required operational current density, aminimum number of nanowires can be included in the thin film ofnanowires for a given area on the substrate. Hence, each formedsemiconductor device will have a sufficient number of nanowires to carrycurrent at an operational current level. For example, the requirednumber of nanowires per unit area can be 1 nanowire, 2 nanowires, andany other greater number of nanowires, including 5, 10, 100 or more.

In another aspect, a thin film of nanowires 100 can be formed to haveasymmetric mobility. For example, this can be accomplished byasymmetrically aligning the nanowires of thin film of nanowires 100,and/or by doping the nanowires in a particular manner. Such asymmetricmobility can be caused to be much greater in a first direction than in asecond direction. For example, asymmetric mobilities can be created inthe order of 10, 100, 1000, and 10000 times greater in the firstdirection than in the second direction, or to have any other asymmetricmobility ratio between, greater, or less than these values.

The nanowires of thin film of nanowires 100 can be doped in various waysto modify performance and for device fabrication. The nanowires can bedoped prior to inclusion in semiconductor device 200, or afterinclusion. The nanowires can be doped during growth and synthesis, priorto being formed into a thin film, after being formed into a thin film orwhen embedded in a composite. A thin film of nanowires can be dopedafter being formed on the substrate. Furthermore, a nanowire can bedoped differently along portions of its long axis, and can be dopeddifferently from other nanowires in thin film of nanowires 100. Someexamples of doping schemes for individual nanowires, and for thin filmsof nanowires are provided as follows. However, it will be apparent topersons skilled in the relevant art(s) from the teachings herein thatnanowires, and thin films thereof, can be doped according to additionalways, and in any combination of the ways described herein.

FIG. 3A shows a single crystal nanowire 300. Nanowire 300 can be dopedor undoped. Nanowire 300 can be doped uniformly or non-uniformly. Singlecrystal nanowires can be doped into either p- or n-type semiconductorsin a fairly controlled way for device fabrication. The type of dopantand dopant concentration in nanowire 300 can be changed to tune theoperating characteristics of a device. Carrier mobility in nanowire 300,threshold voltage for device switching and off-state current flow areall effected by the type and concentration of doping. Carrier mobilitylevels up to 1500 cm²/V_s have been shown for single p-type Si (silicon)nanowires, and carrier mobility levels up to 4000 cm²/V_s have beenshown for n-type InP nanowires.

FIG. 3B shows a nanowire 310 doped according to a core-shell structure.As shown in FIG. 3B, nanowire 310 has a doped surface layer 302, whichcan have varying thickness levels, including being only a molecularmonolayer on the surface of nanowire 310. Doping concentration can varythroughout the thickness of shell surface layer 302. Such surface dopingcan separate impurities from conducting core 300 and decrease theprobability of impurity-related scattering events at the interface ofcore 300 and shell 302. This core-shell architecture may lead to greatlyenhanced carrier mobility inside nanowire core 300 or at its interfacewith shell 302. Ballistic transport may be achieved inside nanowire 310when no scattering occurs and the distance between source and gainelectrodes is no greater than the length of nanowire 310. Further detailon doping of nanowires is provided below. For transistor-type devicefabrication, a dielectric layer and gate are also deposited on nanowire310.

FIG. 3C shows a nanowire 320 that is coated with a dielectric materiallayer 304, according to another type of core-shell structure. Dielectricmaterial layer 304 can be chosen from a variety of dielectric materials,such as SiO₂ or Si₃N₄. The use of dielectric material layer 304 can actas a protective layer in semiconductor device 200, for example, byreducing leakage and preventing electrical shorts. In another example,the dielectric layer can act as a gate dielectric in a field effecttransistor (FET). The dielectric layer can be formed by oxidizing thenanowire, coating the nanowire, or otherwise forming the dielectriclayer. For example, other high dielectric constant materials can beused, including silicon nitride, Ta₂O₅, TiO₂, ZrO₂, HfO₂, Al₂O₃, AlN,AlO, SiC and others, including organic materials, for example, perylene.Nitridation of nanowires can be accomplished with processes similar tothose employed in oxidation of nanowires. These materials can be appliedto nanowires by gas-phase deposition processes, including, but notlimited to, chemical vapor deposition (CVD), plasma assisted chemicalvapor deposition (PACVD) and physical vapor deposition (PVD); solutionphase over-coating or simply by spin-coating the appropriate precursoronto the substrate. Vapors of the dielectric can be prepared by anymethod known in the art, including those employing molten dielectric orvapors created by high voltage discharge or sputtering of thedielectric. Other known techniques can be employed.

FIG. 3D shows a nanowire 330 with core 300 and with a doped shellsurface layer 302 according to the core-shell structure shown in FIG.3B. Nanowire 330 is also coated with a dielectric material layer 304, asshown in FIG. 3C. Shell material 302 should have a bandgap higher thanthat of core material 300. For example, when GaAs nanowires are used forcore 300, GaAlAs can be used for doped shell 302. Doped shell 302 hasthickness less than the diameter of core 300. Dielectric layer 304 isnot doped and has thickness in the range of about 5 nanometers to about100 nanometers.

FIG. 3E shows a nanowire 340 with core-shell-dielectric architecture ofFIG. 3D, and with a gate layer 306 coated over dielectric layer 304.Preferably, dielectric layer 304 is formed on the surface of thenanowire-material composite such that the distance between the gate andnanowire 300 is 5 nanometers or less, 10 nanometers or less, 50nanometers or less, or 100 nanometers or less.

FIGS. 4A and 4B show examples of semiconductor device 200, according toexample doping embodiments of the present invention. As shown in FIG.4A, the top surface of substrate 208 is coated with a dopant layer 402.Dopant layer 402 includes electron-donor or electron acceptor dopingmaterials. Properties of semiconductor device 200 can be controlled bythe introduction of dopant layer 402. The electron-donor or electronacceptor materials introduce negative or positive charge carriers intothe nanowires to achieve n- or p-channel transistors, respectively. Veryhigh mobility levels can be attained in this configuration forsemiconductor device 200 because the dopants are separated from theactual conducting channel.

As shown in FIG. 4B, dopant layer 402 covers a region of substrate 208substantially localized around thin film of nanowires 100. Inembodiments, dopant layer 402 applied to semiconductor device 200 can bepatterned to have two or more areas doped according to different n- andp-type characteristics. For example, in the embodiment of FIG. 4B,dopant layer 402 has a first portion 404 doped with an n-typecharacteristic, and a second portion 406 doped with a p-typecharacteristic. In such an embodiment, a p-n junction can be achievedaccording to a variety of electronic and optoelectronic devices,including light-emitting diodes (LEDs). Electronic devices other thandevice 200 can be fabricated using the method described above. Forexample, a diode can be fabricated as shown in FIG. 4B, although thediode would have electrodes 202 and 206, as gate electrode 204 would notbe necessary. Doped areas can vary in dopant type, size and positionthroughout the device as is necessary in the fabrication particulardevices.

As described above, dopant layer 402 can be introduced on substrate 208prior to or after actual fabrication of semiconductor device 200.

Collections of nanowires manufactured with these materials are usefulbuilding blocks for high performance electronics. A collection ofnanowires orientated in substantially the same direction will have ahigh mobility value. Furthermore, nanowires can be flexibly processed insolution to allow for inexpensive manufacture. Collections of nanowirescan be easily assembled onto any type of substrate from solution toachieve a thin film of nanowires. For example a thin film of nanowiresused in a semiconductor device can be formed to include 2, 5, 10, 100,and any other number of nanowires between or greater than these amounts,for use in high performance electronics.

Note that nanowires can also be used to make high performance compositematerials when combined with polymers/materials such as organicsemiconductor materials, which can be flexibly spin-cast on any type ofsubstrate. Nanowire/polymer composites can provide properties superiorto a pure polymer materials. Further detail on nanowire/polymercomposites is provided below.

As described above, collections or thin films of nanowires can bealigned into being substantially parallel to each other, or can be leftnon-aligned or random. Non-aligned collections or thin films ofnanowires provide electronic properties comparable or superior topolysilicon materials, which typically have mobility values in the rangeof 1-10 cm²/Vs.

Aligned collections or thin films of nanowires provide for materialshaving performance comparable or superior to single crystal materials.Furthermore, collections or thin films of nanowires that include alignedballistic nanowires (e.g., core-shell nanowires as shown in FIG. 3B) canprovide dramatically improved performance over single crystal materials.

Aligned and non-aligned, and composite and non-composite thin films ofnanowires can be produced in a variety of ways, according to the presentinvention. Example embodiments for the assembly and production of thesetypes of thin films of nanowires are provided as follows.

Randomly oriented thin films of nanowires can be obtained in a varietyof ways. For example, nanowires can be dispersed or suspended into asuitable solution. The nanowires can then be deposited onto a desiredsubstrate using spin-casting, drop-and-dry, flood-and-dry, ordip-and-dry approaches. These processes can be undertaken multiple timesto ensure a high degree of coverage. Randomly oriented thin films ofnanowires/polymer composites can be produced in a similar way, providingthat the solution in which the nanowires are dispersed is a polymersolution.

Aligned thin films of nanowires can be obtained in a variety of ways.For example, aligned thin films of nanowires can be produced by usingthe following techniques: (a) Langmuir-Blodgett film alignment; (b)fluidic flow approaches, such as described in U.S. Ser. No. 10/239,000,filed Sep. 10, 2002, and incorporated herein by reference in itsentirety for all purposes; and (c) application of mechanical shearforce. For example, mechanical shear force can be used by placing thenanowires between first and second surfaces, and then moving the firstand second surfaces in opposite directions to align the nanowires.Aligned thin films of nanowires/polymer composites can be obtained usingthese techniques, followed by a spin casting of the desired polymer ontothe created thin film of nanowires. For example, nanowires may bedeposited in a liquid polymer solution, alignment can then be performedaccording to one of these or other alignment processes, and the alignednanowires can then be cured (e.g., UV cured, crosslinked, etc.). Analigned thin film of nanowires/polymer composite can also be obtained bymechanically stretching a randomly oriented thin film ofnanowires/polymer composite.

Thin films of nanowires can be formed on virtually any substrate type,including silicon, glass, quartz, polymeric, and any other substratetype describe herein or otherwise known. The substrate can be large areaor small area, and can be rigid or flexible, such as a flexible plasticor thin film substrate type. Furthermore, the substrate can be opaque ortransparent, and can be made from a conductive, semiconductive, or anon-conductive material.

Nanowire film contacts, including sources, drains, and gates, forexample, can be patterned on a substrate using standardphotolithography, ink-jet printing, or micro-contact printing processes,for example, or by other processes.

A dielectric layer can be applied to a thin film of nanowires on asubstrate to electrically insulate gate contacts, for example. Thesematerials can be applied to nanowires by gas-phase deposition processes,including, but not limited to, chemical vapor deposition (CVD), plasmaassisted chemical vapor deposition (PACVD) and physical vapor deposition(PVD); solution phase over-coating or simply by spin-coating theappropriate precursor onto the substrate. Other known techniques can beemployed, for example, sputtering and others. Such a deposition of adielectric layer on a substrate may not be necessary if the nanowiresare insulated by their own dielectric layer.

Note that nanowire films can be patterned on a substrate using variousprocesses, including lithography techniques. Deposition and patterningof thin film of nanowires can be done simultaneously using variousprocesses, such as ink-jet printing or micro-contact printing methods.

Note that the order in which contacts are patterned can be varied. Forexample, gates 204, sources 202, and drains 206 shown in FIG. 2 can bepatterned simultaneously with each other, or at different times. Theycan be all be patterned prior to deposition of the thin film ofnanowires 100, or afterwards. Sources 202 and drains 206 can bepatterned prior to deposition of the thin film of nanowires 100, whilegates 204 are patterned afterwards. Alternatively, gates 204 can bepatterned prior to deposition of the thin film of nanowires 100, whilesources 202 and drains 206 are patterned afterwards. Either of sources202 and drains 206 can also be patterned prior to deposition of the thinfilm of nanowires 100, while the other is patterned afterwards.

Note that in some embodiments, more than one layer of a thin film ofnanowires can be applied to a substrate in a given area. The multiplelayers can allow for greater electrical conductivity, and can be used tomodify electrical characteristics of a respective semiconductor device.The multiple layers can be similar, or different from each other. Forexample, two or more layers of thin films of nanowires having nanowiresaligned in different directions, doped differently, and/or differentlyinsulated, can be used in a particular semiconductor device. A contactarea of a particular semiconductor device can be coupled to any one ormore of the layers of a multiple layer thin film of nanowires. Note thata thin film of nanowires can be formed as a monolayer of nanowires, asub-monolayer of nanowires, and greater than a monolayer of nanowires,as desired.

Example Applications of Nanowire Films of the Present Invention NanowireComposite Embodiments

In another aspect, the invention relates to a system and process forproducing a nanowire-material composite. For example, FIG. 5 shows aflowchart 500 showing example steps for producing a nanowire-materialcomposite, according to an embodiment of the present invention. FIGS.6A-6C show example implementations of the steps of FIG. 5. Flowchart 500begins with step 502. In step 502, a substrate having nanowires attachedto a portion of at least one surface is provided. In step 504, amaterial is deposited over the portion to form the nanowire-materialcomposite. Flowchart 500 optionally further includes step 506. In step506, the nanowire-material composite is separated from the substrate toform a freestanding nanowire-material composite.

FIG. 6A shows an example implementation of step 502. Referring to FIG.6A, a substrate 602 is provided having nanowires 606 attached to aportion 604. Portion 604 can be all or less than an entire area of asurface of substrate 602. It is understood by one of ordinary skill inthe art that nanowires can be prepared by a variety of methods.Nanowires for use in the present invention can be prepared by any methodknown in the art. Particular methods are exemplified in U.S. Pat. No.5,997,832, U.S. Pat. No. 6,036,774 and published U.S. Patent Appl. No.20030089899, all of which are incorporated herein by reference in theirentireties for all purposes. The nanowires are prepared on a substrateand attached to the substrate. For example, nanowires 606 can be grownon substrate 602; or can be grown separately and subsequently attached.The substrate can be any material upon which nanowires can be prepared.Examples of suitable substrates for substrate 602 include, but are notlimited to: silicon and silicon oxide-coated silicon wafers, glass,ceramic, polymeric wafers and a composite thereof. Alternatively,substrate 602 can be the interior and/or exterior surfaces of a tube, acube or sphere, or other three dimensional object. Substrate 602 canalso be an irregular object or porous medium, such as a reticulatedmacroporous metal, oxide or ceramic. In one particular example, themethod of gold nanoparticle catalyzed chemical vapor deposition (CVD)grows nanowires on a silicon wafer substrate such that the nanowires arerandomly aligned or have no alignment.

Alternatively, the gold, or other material, nanoparticles are depositedon the interior and/or exterior surfaces of a three dimensional object,such as an object made from a macroporous metal and/or oxide. The objectis immersed in a solution comprising the nanoparticles and thenanoparticles adhere or bind to the surface of the object. For example,the nanoparticles bind to the surface by static charge.

FIG. 6B shows an example implementation of step 504. Referring to FIG.6B, a material 608 is deposited over portion 604 to form ananowire-material composite. The material for use as material 608 in thepresent invention can be any material capable of forming a compositewith nanowires 606. The particular choice of material is dependent onthe intended application of the nanowires and the nanowire-materialcomposite. Particular examples include but are not limited to polymericmaterials, glasses and ceramics. Preferred materials for materials 608include materials that can be separated from the substrate and formfreestanding nanowire-material composites. Preferred materials includeflexible materials, including, but not limited to polymers and resins.Furthermore, preferred materials for materials 608 are capable ofadhering to and supporting the nanowires while the nanowire-materialcomposite is separated from the substrate such that the nanowires aredetached from the substrate and become embedded in the composite intactand undamaged from the separation.

It is understood by one of ordinary skill in the art that suitablepolymers for material 608 include, but are not limited to an elastomer,thermoplastic or thermosetting resin. Particularly, polymers for useinclude oligomers, which includes, but is not limited to monomers,dimers, trimers, tetramers, pentamers, hexamers, heptamers, octamers,nonamers, decamers, undecamers, and dodecamers; branched, hyperbranched,dendritic and other non-linear structural forms of polymers; prepolymerssuch as phenoxy and epoxy prepolymers; networked polymers such asinterpenetrating and semi-interpenetrating network polymers;homopolymers, copolymers, terpolymers and other copolymers includingrandom, statistical, alternating, block and graft copolymers and blendsof two or more different polymers. Particular examples of polymers foruse in material-nanowire composites include, but are not limited topolyalkanes, polyhaloalkanes, polyalkenes, polyalkynes, polyketones,polycarbonates, polyamides, polyimides, polyarylenes, polyarylvinylenes,polyheteroarylenes, polyheteroarylvinylenes polyesters, polyethers,polyurethanes, polybenzimidazoles, polysulfides, polysiloxanes,polysulfones, polysaccharides, polypeptides, polyphosphazenes,polyphosphates, phenolic and phenol-formaldehyde resins, epoxy andphenoxy resins, and urea- and melamine-formaldehyde resins.

The nanowire-material composite shown in FIG. 6B optionally comprisesadditives to modify the properties of the material 608. One example ofan additive is a plasticizer. Plasticizer is used herein to mean anymaterial that can decrease the flexural modulus of a polymer. Theplasticizer may influence the morphology of the polymer and may affectthe melting temperature and glass transition temperature. Examples ofplasticizers include, but are not limited to: small organic andinorganic molecules, oligomers and small molecular weight polymers(those having molecular weight less than about 50,000), highly-branchedpolymers and dendrimers. Specific examples include: monomericcarbonamides and sulfonamides, phenolic compounds, cyclic ketones,mixtures of phenols and esters, sulfonated esters or amides,N-alkylolarylsulfonamides, selected aliphatic diols, phosphite esters ofalcohols, phthalate esters such as diethyl phthalate, dihexyl phthalate,dioctyl phthalate, didecyl phthalate, di(2-ethylhexy)phthalate anddiisononyl phthalate; alcohols such as glycerol, ethylene glycol,diethylene glycol, triethylene glycol, oligomers of ethylene glycol;2-ethylhexanol, isononyl alcohol and isodecyl alcohol, sorbitol andmannitol; ethers such as oligomers of polyethylene glycol, includingPEG-500, PEG 1000 and PEG-2000; and amines such as triethanol amine.

Examples of other additives for use in the invention include but are notlimited to fillers, antioxidants, colorants, initiators, crosslinkingand curing agents, impact strength modifiers, heat and ultravioletstabilizers, flame retardants, antistatic agents, electrical and thermalconductivity modifiers, drugs and biologically active compounds andmolecules.

Referring to FIG. 6B, material 608 is deposited over portion 604 usingany method that allows for the controlled deposition of material 608. Itis understood by one of ordinary skill in the art that many differentmethods of deposition are available and the choice of method depends onthe type of material 608 used and the desired final properties of thenanowire-material composite. Methods for depositing material 608include, but are not limited to drop-casting, spin-coating, dip-coating,langmiur-blodgett techniques and blade coating. It is understood by oneof ordinary skill in the art that material 608 can be deposited in avariety of forms. The forms include, for example, but are not limited toa neat liquid or melt and as a solution in a suitable solvent. Suitablesolvents include aqueous and non-aqueous solvents.

In a preferred method for deposition, material 608 is depositedunidirectionally such that nanowires 606 are substantially alignedparallel to their long axis as a result of the deposition. For example,material 608 is made to flow over nanowires 606 such that nanowires 606are substantially aligned parallel to the direction of flow.Alternatively, material 608 is deposited by blade coating by movingsubstrate 602 and/or the blade in such a way that results in thesubstantial alignment of nanowires 606 parallel to their long axis andparallel to the direction of movement. Alternatively, substrate 602having nanowires 606 attached thereon is dipped into a bath of material608 or a langmuir-blodgett trough. Substrate 602 is removed such thatnanowires 606 are substantially aligned parallel to their long axis andparallel to the direction that substrate 602 is removed from the bath.It will be apparent to one of ordinary skill in the art that alternativemeans of aligning the nanowires during deposition of material 608 areavailable. Alternative means include, for example, electric and/ormagnetic field alignment.

After depositing material 608 over portion 604, material 608 isoptionally further processed. A variety of processing steps can beperformed, depending on the desired final properties of thenanowire-material composite. Processing steps include, but are notlimited to hardening, curing, cross-linking, polymerizing, photopolymerizing, melting, crystallizing, oxidizing and reducing.

In one particular example, referring back to FIG. 6B, material 608 isdeposited over portion 604 as a polymer solution. Examples of polymersolutions for use in the present invention include, but are not limitedto polystyrene, poly(methylmethacrylate), nylon-6 or poly(ethyleneterephthalate) dissolved in toluene; polyethylene or polypropylenedissolved in dichloromethane; and poly(lactic acid) dissolved in water.Removing the solvent from material 608 hardens material 608 and formsthe nanowire-material composite. The solvent can be removed by anymethod known to one of ordinary skill in the art, for example, byevaporating the solvent.

In another example, material 608 is deposited over portion 604, as amixture of at least one or more prepolymers. Processing the mixture bypolymerizing the prepolymers forms the material-nanowire composite. In aparticular example, low-molecular weight polyurethane oligomers aredeposited as a neat film and heat-cured to form a high-molecular weightelastomeric polyurethane composite having nanowires embedded therein. Ina further example, a mixture of two or more epoxy prepolymers isdeposited over the nanowires as a neat film, or two or more epoxyprepolymers are deposited separately and admixed on the substrate toform an epoxy polymer. Curing the film forms an epoxy resin compositehaving nanowires embedded therein. In another example, a monomer film,neat or with additives, such as initiator, e.g. a photoinitiator orheat-activated initiator, is deposited over the nanowires. Polymerizingthe monomer film using heat, light, x-rays, microwaves or otherelectromagnetic energy forms the material-nanowire composite. Depositinga mixture of different monomers, neat or with additives, such asinitiator, and polymerizing the mixture, forms the material-nanowirecomposite having an interpenetrating and/or semi-interpenetratingnetwork polymer as the base material.

In another example, material 608 is deposited on the interior surface(s)of an irregular object. Any method of deposition can be used. Forexample, a substrate can comprise reticulated macroporous metals such asaluminum, that have nanowires attached on the interior of the pores ofthe metal. The macroporous substrate is then impregnated or injectedwith material 608. Upon impregnation or injection, material 608 coversthe portions of the substrate to which the nanowires are attached. Thematerial covering the nanowires can optionally be further processed, asdescribed herein.

In an embodiment, after forming the nanowire-material composite, it isoptionally further processed while attached to substrate 602.Alternatively, the nanowire-material composite is separated fromsubstrate 602 before optional further processing. Optional furtherprocessing steps include, but are not limited to, planarization,patterning, separating the patterned nanowire-material composite fromsubstrate 602, doping, metallization and further device fabricationsteps.

FIG. 6C shows an example implementation of step 506. Referring to FIG.6C, after forming the nanowire-material composite the composite isseparated from substrate 602 to form freestanding nanowire-materialcomposite 610. It is understood that a variety of methods are availableto separate nanowire-material composite from substrate 602. Preferably,the method of separation results in a freestanding nanowire-materialcomposite 610, wherein the nanowires are detached from substrate 602 andare embedded in material 608 intact, without being damaged duringseparation. Methods of separating nanowire-material composite 610 fromsubstrate 602 for use in the present invention include, but are notlimited to the three following examples.

First, using a blade, nanowire-material composite 610 is physicallylifted from substrate 602. The term blade is used herein to refer to anysharp-edged object capable of lifting composite 610 off of substrate 602and detaching nanowires 606 from substrate 602 without damagingnanowires 606. The blade is used to separate the entire composite 610from the substrate, or alternatively, the blade is used to separate afirst portion of composite 610 from substrate 602. A second portion ofcomposite 610 is mechanically separated from substrate 602 or liftedfrom the substrate by hand or hand-held apparatus.

Second, substrate 602 is etched away from nanowire-material composite610. The method of etching substrate 602 depends on the material ofsubstrate 602. For example, plasma etching is used to etch away asilicon wafer substrate from a nanowire-material composite 610.Alternatively, the silicon wafer substrate is chemically etched awayfrom composite 610 using a suitable etching agent, such as hydrofluoricacid and an oxidizing agent such as HNO₃ or H₂SO₄. Other chemicaletching agents include, but are not limited to, KOH and XeF₂. Metalsubstrates can be electrochemically etched away from nanowire-materialcomposite 610. Polymeric substrates can be separated fromnanowire-material composite 610 by dissolving the substrate in asuitable fluid that does not dissolve nanowire-material composite 610.

Third, a parting layer is used to separate the nanowire-materialcomposite 610 from substrate 602. The term parting layer is used hereinto refer to any agent capable of facilitating the separation ofnanowire-material composite 610 from substrate 602. An example of aparting layer for use in the present invention includes, but is notlimited to, a chemically removable parting layer between substrate 602and nanowire-material composite 610. For example, substrate 602 is firstcoated and/or covered on at least one surface with a chemicallyremovable parting layer. Nanowires 606 are grown on the chemicallyremovable parting layer. Material 608 is deposited over nanowires 606 toform nanowire-material composite 610. The nanowire-material composite610 is separated from substrate 602 by dissolving the chemicallyremovable layer in a suitable solvent. The suitable solvent is capableof dissolving the chemically removable layer but does not dissolvenanowire-material composite 610 or the substrate. The parting layer canalso be a photoremovable layer, in which ultraviolet or other suitablewavelengths of light, or other suitable electromagnetic energy, are usedto remove the parting layer and separate nanowire-material composite 610from substrate 602. An example of a photoremovable layer is a substancethat breaks down and disintegrates in the presence of ultraviolet light,making it easily removed by washing with a suitable fluid.

In an embodiment of the invention, the freestanding nanowire-materialcomposite 610 is collected in sheets and can be stored for later use.Flexible nanowire-material composites 610 are optionally rolled andstored for later use or for further optional processing.

In an embodiment, the freestanding nanowire-material composite 610 isfurther optionally processed. Alternatively, material 608 is separatedfrom nanowires 606 and nanowires 606 are harvested for furtherprocessing. Any method capable of separating material 608 from nanowires606 can be used in the present invention. Specific examples include, butare not limited to dissolving material 608 in a suitable solvent,heating the nanowire-material composite 610 to a temperature sufficientto incinerate material 608, and etching away the material. Suitablesolvents include those fluids that dissolve material 608 while leavingnanowires 606 intact and undamaged. The solvent contactsnanowire-material composite 610, dissolves material 608 and nanowires606 are collected by some means, for example filtration. Heatingnanowire-material composite 610 can be done in any suitable furnace.Nanowires 606 are washed free of any ash from material 608 andcollected. Etching away material 608 can be done with a plasma etch orother ion-etch that is capable of separating nanowires 606 from material608. The collected nanowires 606 can be optionally further processedinto thin films for electronic device fabrication.

Embodiments for Depositing Oriented Nanowires

In an embodiment, the invention relates to a system and process fordepositing oriented nanowires. For example, FIG. 7 shows a flowchart 700showing example steps for depositing oriented nanowires according to anembodiment of the present invention. FIGS. 8A-8F show exampleimplementations of the steps of FIG. 7. Flowchart 700 begins with step702. In step 702, a first substrate having nanowires attached to aportion of at least one surface is provided, wherein each nanowire has afirst end attached to said portion. Preferably, the nanowires areoriented substantially perpendicular to the surface of the substrate. Instep 704, a material is deposited over the portion to form ananowire-material composite. In step 706, the nanowire-materialcomposite is patterned to form a patterned composite. In step 708, thepatterned composite is separated from the first substrate. In step 710,the patterned composite is applied to a second substrate such that thenanowires are aligned substantially parallel to the second substrate.

FIG. 8A shows an example implementation of step 702. Referring to FIG.8A, before step 702, nanowires 804 are grown on a first substrate 802.Preferably, nanowires 804 are grown perpendicular to the surface ofsubstrate 802. Any method known in the art can be used to grow nanowiresperpendicular to a surface, including, for example, the methodsdescribed in U.S. Pat. No. 6,996,147, which is incorporated herein, inits entirety, for all purposes. Preferably, nanowires 804 are grown to alength 811, which can be in the range of about 10 to about 20 micronsalthough the invention is not limited to this range. Preferably,nanowires 804 are grown such that a portion 805 of each nanowire at anend that is attached to substrate 802 is doped. Methods for dopingnanowires are well known in the art. Any method of doping can be usedduring growth that results in portion 805, which is attached to thesubstrate, being doped.

Flowchart 700 can optionally include providing a parting layer on thefirst substrate, wherein the nanowires are attached to a portion of saidparting layer. Nanowires 804 are optionally doped at the end that isattached to the parting layer. The parting layer facilitates theseparation of nanowires 804 from substrate 802.

FIG. 8B shows an example implementation of step 704. Referring to FIG.8B, material is deposited over the portion to form a nanowire-materialcomposite 806. The material is deposited over the nanowires, to a height807 such that the nanowires are covered by the material and embedded innanowire-material composite 806. As discussed above, any method known inthe art for depositing the material over the nanowires can be used inthe present invention. After the material is deposited over thenanowires, the material is optionally processed to formnanowire-material composite 806. Optional processing steps are discussedabove. Preferably, the material is polymerized or cross-linked in acuring and/or hardening step. Preferably, the material isphotopolymerized and/or heat-cured to form nanowire-material composite806.

FIG. 8C shows an example implementation of step 706. Referring to FIG.8C, the nanowire-material composite is patterned to form patternedcomposite 808. Optionally, the nanowire-material composite is patternedinto a plurality of patterned composites 808. The nanowire-materialcomposite can be patterned into any shape. Preferably, thenanowire-material composite is patterned into a plurality ofsubstantially rectangular blocks 808. Blocks 808 can be patterned tohave any dimensions, depending on the particular application. A height809 of block 808 is about equal to or greater than the length of thenanowires, which would result in the nanowires being completely embeddedin each composite block. Alternatively, the nanowires are not completelyembedded in block 808, such that the height 809 of the block 808 is lessthan the length, 811, of the nanowires, leaving a portion 813 notembedded in block 808. The height 809 of the blocks 808 can range fromabout 2 microns to about 50 microns, although the invention is notlimited to this range. Preferably, the blocks have a height of less thanabout 10 microns. The plurality of blocks can be uniform in dimensions,or alternatively, the blocks are patterned such that each block, or eachgroup of blocks, has different dimensions. Methods for patterningmaterials are well known in the art. Any method that results in awell-defined pattern of nanowire-material composite can be used in thepresent invention. A method of patterning for use in the presentinvention includes, but is not limited to, lithographic patterning,including, but not limited to, photolithography and soft lithography.Alternatively, the method of patterning can be reactive ion etching.Such etching, in accordance with the invention include, but are notlimited to, ions of SF₆, CF₄, CHF₃, CCl₄, CCl₂F₂, Cl₂, O₂, H₂ and Ar.

FIG. 8D shows an example implementation of step 708. Referring to FIG.8D, the patterned blocks 808 are separated from substrate 802. Asdescribed above, any method of separation can be used. Referring to FIG.8D, the blocks, once separated, form freestanding nanowire-materialblocks 810, and can be stored for later use and further optionalprocessing. Preferably, the blocks are further processed on a secondsubstrate.

FIG. 8E shows an example implementation of step 710. Referring to FIG.8E, freestanding nanowire-material blocks 810 are laminated to a secondsubstrate 814 such that the nanowires are substantially parallel to thesurface of the second substrate. For example, a plurality ofnanowire-material blocks 810 can be laminated on substrate 814 in apredetermined pattern. Alternatively, blocks 810 are arranged onsubstrate 814 in no pattern or in a random pattern. Any method known toone of ordinary skill in the art can be used to laminate blocks 810 tothe second substrate 814. The choice of method depends on factors suchas the material in block 810 and the type of substrate 814. For example,blocks 810 can be designed to adhere to substrate 814 through covalentand/or non-covalent bonds. For example, composite blocks 814 can be madefrom a pressure-sensitive adhesive polymer that adheres to substrate 814when blocks 810 are arranged on its surface and pressure is applied.Alternatively, a separate adhesive can be used to laminate blocks 810 tosubstrate 814. Adhesives are well known in the art and the choice ofadhesive depends on the particular application and the material of block810 and substrate 814. Alternatively, blocks 810 can be laminated tosubstrate 814 via covalent chemical bonds. Any method of producing thecovalent chemical bond can be used. For example, the covalent chemicalbond can be a siloxane bond. One of ordinary skill in the art will knowhow to produce a siloxane bond between block 810 and substrate 814. Forexample, a reaction between hydroxyl groups and halosilanes can be used.

FIG. 8F shows an example implementation of an optional furtherprocessing step. The nanowire-material blocks are optionally planarizedto form planarized blocks 814 and 816. In an embodiment, allnanowire-material blocks laminated to the second substrate areplanarized to the same height. Alternatively, a first plurality ofnanowire-material blocks 814 are planarized to a first height and asecond plurality of nanowire-material blocks 816 are planarized to asecond height. Alternatively, the nanowire-material blocks areplanarized individually to different heights. In further embodiments,one or more nanowire-material blocks laminated to the second substrateare not planarized. Any method known to one of ordinary skill in the artcan be used to planarize the nanowire-material blocks. Preferably,oxygen plasma is used to planarize the nanowire-material blocks.

Planarization removes material from the nanowire-material composite.Preferably, the planarization exposes at least one surface of at leastone nanowire. Alternatively, the planarization removes all the materialfrom the nanowire-material composite and exposes the nanowires that wereembedded in the composite. When it is desired to remove all the materialduring planarization, nanowire-material blocks can be optionallydetached from the substrate after a first surface of at least onenanowire is exposed. The detached block can then be turned over andre-attached to the substrate and further planarized to expose all othersurfaces of the nanowires. This allows for the complete removal of allthe material from the nanowire-material composite block and results in aneat thin film of nanowires that are substantially aligned parallel totheir long axis and parallel to the surface of the substrate.Alternatively, planarization can remove material and yet not expose anysurface of the nanowires.

In an embodiment, the planarization results in a plurality of blocks ofexposed nanowires that are patterned on a surface of a substrate. Theexposed nanowires are optionally further processed to produce electronicdevices. Optional further processing steps include, but are not limitedto coating with a dielectric layer, doping, patterning, planarization,metallization and further device fabrication steps.

To fabricate a device, for example, the nanowire-material blocks can beplanarized on the second substrate to remove the material from theblock. A thin film of nanowires is thereby formed on the secondsubstrate having nanowires aligned substantially parallel to the secondsubstrate, with a sufficient density to achieve an operational currentlevel. A plurality of semiconductor device regions can be defined in thethin film of nanowires. Contacts are formed at the semiconductor deviceregions to thereby provide electrical connectivity to the plurality ofsemiconductor devices.

Further optional processing steps also include laminating one or moreadditional nanowire-material composite blocks on the first planarizedblocks 814 and 816, to produce layered blocks. Optional processing stepscan be performed on each layer individually or in groups.

Electronic Substrate Embodiments

In an embodiment, the present invention relates to a system and processfor producing an electronic substrate. For example, FIG. 9 shows aflowchart 900 showing example steps for producing an electronicsubstrate, according to an embodiment of the present invention. FIG. 10shows a flowchart 1000 showing optional steps that can be performedafter step 906, and before step 908. FIG. 11A through FIG. 18B showexample implementations of the steps for FIG. 9 and FIG. 10.

Flowchart 900 begins with step 902. In step 902, a nanowire-materialcomposite comprising a plurality of nanowires is attached to a portionof a substrate. In step 904, the nanowire-material composite isoptionally planarized to expose a portion of the nanowires. In step 906,the nanowire-material composite is patterned to define one or moresemiconductor device regions. In step 908, contacts are formed at thesemiconductor device regions to thereby provide electrical connectivityto said device regions.

Flowchart 1000 begins with step 1002. In step 1002, a dielectric layeris optionally deposited on the nanowire-material composite. In step1004, the dielectric layer is optionally etched to form a pattern of thedielectric layer and to form a pattern of exposed nanowire-materialcomposite to define the one or more semiconductor device regions. Instep 1006, the exposed nanowire-material composite is optionally doped.In step 1008, the dielectric layer is optionally removed before step 908of forming contacts.

FIGS. 11A and 11B show an example implementation of step 902. FIG. 11Ashows a plan view of a nanowire-material composite 1102 laminated onsurface of a substrate. Composite 1102 has nanowires 1104 embedded in amaterial 1106 in sufficient density to achieve an operational currentlevel. FIG. 11B shows a side view of composite 1102 laminated to the topsurface of substrate 1108. Multiple layers of nanowires 1104 areembedded in material 1106. Alternatively, a single layer of nanowires isembedded in the material. Preferably, nanowires 1104 are alignedsubstantially parallel to their long axis and parallel to the surface ofthe substrate to which composite 1102 is laminated. After laminatingcomposite 1102 to substrate 1108, the composite can be optionallyplanarized to expose a surface of a layer of nanowires.

FIGS. 12A and 12B show an example implementation of step 904. FIG. 12Ashows a plan view of nanowire-material composite 1102 having nanowires1104 embedded in material 1106. FIG. 12B is a side view showingnanowire-material composite 1102 laminated to substrate 1108 and havingnanowires 1104 embedded in material 1106, and having a surface exposeddue to planarization. After optionally planarizing composite 1102, thecomposite can be patterned into a predetermined pattern.

FIGS. 13A and 13B show an example implementation of step 906. FIG. 13Ais a plan view showing patterned nanowire-material composite 1302 havinga square shape and having nanowires 1104 embedded in material 1106. Thenanowire-material composite can be planarized into any shape, or intoany pattern of a plurality of like or different shapes. Alternativeshapes include, but are not limited to, circles, rectangles, triangles,rings, ovals, stars, any other shape or any random pattern. FIG. 13Bshows a side view of patterned nanowire-material composite 1302laminated on substrate 1108 and having nanowires 1104 embedded inmaterial 1106 and having an exposed surface. After forming patternednanowire-material composite 1302, a dielectric layer can be deposited oncomposite 1302 and the exposed surface of substrate 1108.

FIG. 14A and FIG. 14B show an example implementation of step 1002. FIG.14A shows a plan view of dielectric layer 1402 deposited on substrate1108 and patterned nanowire-material composite 1302. FIG. 14B shows aside view of dielectric layer 1402 covering patterned nanowire-materialcomposite 1302, embedded and exposed nanowires 1104, material 1106 andsubstrate 1108. Dielectric layer 1402 can be deposited using any processknown in the art, including for example, drop casting, spin-coating orblade coating of polymeric, oxide or any other dielectrics. Polymerdielectrics for use in the present invention include any polymers,including for example, polyimides, fluorinated polyimides,polybenzimidazoles, and others. Oxide dielectrics for use in theinvention include SiO₂, Ta₂O₅, ZrO₂, Hf₂O, and Al₂O₃. Nitridedielectrics include AlN and SiN. A preferred dielectric material is SiN.

FIGS. 15A and 15B show an example implementation of step 1004. Referringto FIG. 15A, dielectric layer 1402 is etched to form a pattern of thedielectric layer and to form a pattern of exposed nanowire-materialcomposite to define the one or more semiconductor device regions. FIG.15B shows a side view with semiconductor device regions 1502 etched intodielectric layer 1402 to expose a portion of patterned nanowire-materialcomposite 1302. Etching can be done by any method described above,preferably a fluorine based etch plasma or reactive ion etch is used.

FIGS. 16A and 16B show an example implementation of step 1006. As shownin FIGS. 16A and 16B, the exposed nanowire-material composite is dopedto form doped composite 1602 and doped dielectric layer 1604. Doping canbe done by any method known in the art. Preferred methods include, butare not limited to, spin-on-doping, low-energy ion implantation or ionshowering.

FIGS. 17A and 17B show an example implementation of step 1008. As shownin FIG. 17A, dielectric layer 1402 is removed to expose patternednanowire-material composite 1302 and exposed nanowires 1104. Regions ofdoped nanowire-material composite 1602 are also shown. FIG. 17B shows aside view of substrate 1108 having patterned nanowire-material composite1302 laminated to the top surface.

FIGS. 18A and 18B show an example implementation of step 908. Thesemiconductor device regions are metallized to form electricalconnectivity to the device regions. FIG. 18A shows a plan view ofmetallized semiconductor device regions 1802, 1804 and 1806, which formsource, gate and drain transistor electrodes respectively. FIG. 18Bshows a side view of regions 1802, 1804 and 1806. Metallization can becarried out using any method known in the art. Preferably, thesemiconductor device regions are metallized by e-beam evaporation.Preferably, the source and drain electrodes are formed whereby thenanowires form channels having a length between respective ones of thesource and drain electrodes, and the nanowires are aligned approximatelyparallel to an axis between the source and drain contacts. Preferably,the gate electrode is formed on the surface of the nanowire-materialcomposite such that the distance between the gate and the nanowires is 5nanometers or less, 10 nanometers or less, 50 nanometers or less, or 100nanometers or less.

An alternative process for producing an electronic substrate is shown inFIGS. 19A-19E, which show plan views of a substrate. As shown in FIG.19A, a nanowire-material composite 1902 is provided having nanowires1904 embedded in material 1905. Preferably, the nanowires are alignedsubstantially parallel along their long axis. A composite 1902 isoptionally laminated on a surface of a substrate.

As shown in FIG. 19B, a portion of material 1905 is removed from thenanowire-material composite to form areas 1906, in which material 1905has been removed. Material 1905 is removed such that nanowires 1904remain in areas 1906. Composite 1902 is thereby patterned into strips ofnanowire-material composite 1907 having areas 1906, which compriseexposed nanowires.

As shown in FIG. 19C, the composite strips 1907 can be furtherprocessed, for example, by hardening, curing or cross-linking material1905 to form processed strips 1908. The strips 1907 can be planarized toform planarized strips. A dielectric layer can be formed on a portion ofthe exposed nanowires and/or on planarized strips 1907. The portions ofexposed nanowires can be doped in either areas 1906 or on planarizedstrips 1907.

As shown in FIG. 19D, the areas of exposed nanowires can be metallizedto form areas of electrical connectivity and form addressableelectrodes. It is understood by one of ordinary skill in the art that avariety of architectures can be built in the metallization step,depending on which device is desired. For example, metallizing processedstrips 1908 forms metallized substrate 1910. In another example, FIG.19E shows metallized positive electrode 1911 and metallized negativeelectrode 1912 deposited to form a diode 1913. In another example, anodeand cathode electrodes are formed in the metallization step. When avoltage is applied across electrodes 1911 and 1912, a p-n junction formsbetween electrodes 1911 and 1912. The p-n junction is formed in thesemiconductor nanowires 1904, such that light is emitted from thenanowires 1904 during operation. The wavelength of light emitted fromthe nanowire depends on several factors, including the nanowiresemiconductor material and the presence of impurities in the nanowire.The minimum voltage required for the nanowires to emit light alsodepends on these factors. Preferably, the minimum voltage is less thanabout 5 volts. Diode 1913 is separately addressable and has pixel sizedimensions for display applications. Therefore, sheets of composite 1913can be formed that comprise a plurality of independently andelectrically addressable pixel sized diodes for flat-panel displayapplications.

Light Emitting Diode Embodiments

In an embodiment, the present invention relates to a flat-panel displaycomprising as the active layer a Light-Emitting Diode (LED). The LEDcomprises one or more nanowire-material composites having a plurality ofindependently and electrically addressable pixel sized diodes. Eachaddressable diode includes nanowires as the active light-emittingelement.

FIG. 20 shows an example of a multi-layered display 2002 having threedifferent and independent active layers. The layers comprise nanowiresthat emit light at different wavelengths. Preferably, the layer attachedto a substrate 2008 the bottom layer, emits red light. Examples ofred-emitting nanowires are made from GaAsP. The middle layer 2006preferably comprises green-emitting nanowires, for example, InGaNnanowires. The top layer 2004 preferably comprises blue-emittingnanowires, for example, InGaN nanowires. Note, however, the layers canbe arranged in different orders, and can have different numbers oflayers. Other semiconductor nanowire materials for use in light-emittingapplications includes, but is not limited to GaN, GaP, GaAs, InP, InAs,ZnO and combinations thereof.

In an embodiment, the top layer absorbs no light, or alternatively, onlya small amount of light emitted by the two layers below it. In otherwords, in the configuration at FIG. 20, the blue layer does not absorblight emitted from the red or green layer. Also, the green layer doesnot absorb light from the red layer. It is understood by one of ordinaryskill in the art that different colors can be used when stacking layersof light-emitting nanowire-material composites. Color combinationsshould be chosen such that layers laminated on top of another layer donot absorb a substantial amount of the light emitted from the lowerlayer.

FIG. 21 shows an absorption spectra 2102 for a variety of nanowirescompositions. Nanowires absorbing light having wavelengths greater thanabout 1.0 microns should be below layers absorbing light havingwavelengths between about 0.7 and about 1.0 microns. Nanowires absorbinglight having wavelengths between about 0.3 and about 0.7 microns shouldbe laminated on top of all other layers. Alternatively, however, theselayers can be stacked in different orders.

In an embodiment, therefore, the present invention relates to ananowire-material composite, comprising a polymer having nanowiresembedded therein, which emits light. Thus, the present invention may beused in any display and/or light source application, includingtelevisions, computer displays, (e.g., handheld, notebook, desktop,laptop), overhead displays, indoor or outdoor lighting, and any othersuch applications.

Solution Based Processing Embodiments

In an embodiment, the present invention relates to a method of forming ananowire-material composite. FIG. 22 shows flowchart 2200 showingexample steps for producing a nanowire-material composite using solutionbased methods, according to an embodiment of the present invention. Instep 2202, nanowires are contacted with a material to form a mixture.Any material, such as material 608, shown in FIG. 6, can be used to formthe mixture. The formation of the mixture can be facilitated bystirring, sonication or any other method known to one of ordinary skillin the art for dispersing nanowires in the material.

In step 2204, the mixture is deposited on a substrate to form ananowire-material composite. The mixture is deposited using any methodthat allows for the controlled deposition of the mixture. It isunderstood by one of ordinary skill in the art that many differentmethods of deposition are available and the choice of method depends onthe type of material, substrate and nanowires used and the desired finalproperties of the nanowire-material composite. Methods for depositioninclude, but are not limited to drop-casting, spin-coating, dip-coating,langmiur-blodgett techniques and blade coating. It is understood by oneof ordinary skill in the art that the mixture can be deposited in avariety of forms. The forms include, for example, but are not limited toa neat liquid or melt and as a solution in a suitable solvent. Suitablesolvents include aqueous and non-aqueous solvents.

In an example embodiment, the mixture is deposited unidirectionally suchthat the nanowires are substantially aligned parallel to their long axisas a result of the deposition. For example, the mixture is made to flowover the substrate such that the nanowires are substantially alignedparallel to the direction of flow. Alternatively, the mixture isdeposited by blade coating in such a way that results in the substantialalignment of the nanowires parallel to their long axis and parallel tothe direction of movement. Alternatively, the substrate is dipped into abath of the mixture or a langmuir-blodgett trough containing themixture. The substrate is removed such that the nanowires aresubstantially aligned parallel to their long axis and parallel to thedirection that the substrate is removed from the bath. It will beapparent to one of ordinary skill in the art that alternative means ofaligning the nanowires during deposition of the mixture are available.Alternative means include, for example, electric and/or magnetic fieldalignment.

In an exemplary method of aligning nanowires using an electric field,positive and negative electrodes are held across the deposited mixtureor nanowire-material composite. A direct current (DC) electric field isapplied to the mixture or composite in the range of about 10 V/cm toabout 3000 V/cm or other value, and held constant or varied for a timesufficient to align the nanowires.

After depositing the mixture on the substrate, the material isoptionally further processed. A variety of processing steps can beperformed, depending on the desired final properties of thenanowire-material composite. Referring back to FIG. 22, one example isshown in optional step 2206, in which the material is hardened.Alternative processing steps include, but are not limited to curing,cross-linking, polymerizing, photo polymerizing, melting, crystallizing,oxidizing, reducing and removing solvents, gases or other volatilefluids. Solvents or volatile gases and fluids can be removed using anymethod known to one of ordinary skill in the art. Removing volatilegases/fluids can render the composite porous by removing the volatilegases/fluids quickly, or by selectively choosing appropriate volatilegases. Example appropriate volatile gases include inert gases that donot react or interfere with the embedded nanowires, such as nitrogen,helium, argon or the like.

In an embodiment, after forming the nanowire-material composite, it isoptionally further processed while attached to the substrate.Alternatively, the nanowire-material composite is separated fromsubstrate before optional further processing to form a free-standingnanowire-material composite. Optional further processing steps include,but are not limited to, planarization, patterning, separating thepatterned nanowire-material composite from the substrate, doping,metallization and further device fabrication steps.

Nanowire Array Embodiments

In an embodiment, the present invention relates to a nanowire array anda method of producing the same. FIG. 23A shows a flowchart 2300 showingexample steps for producing a nanowire array, according to an embodimentof the invention. In step 2302, a nanowire-material composite isprovided. The composite can be provided on a substrate or as afree-standing composite. The composite can comprise embedded nanowiresthat are oriented in any fashion. For example, the nanowires can beoriented perpendicular to the surface of the substrate or randomlyoriented. The composite can be formed on the substrate, or formed as afreestanding composite and attached to the substrate in subsequentprocessing steps.

In step 2304, a mask is applied to the nanowire-material composite. Themask allows for the controlled removal of a portion of material from thecomposite. For example, the mask is a shadow mask. The mask can be madeof any material that allows for the selective removal of material fromthe composite, for example, metal foil. Metal foils for use as the maskinclude those foils that are inert and unreactive to the composite. Themask comprises an array of shapes that allows for patterns of materialto be selectively removed, for example, the mask comprises an array ofcircles, squares, rectangles or any other regular or irregular shapes orpatterns. In an embodiment, as shown in FIG. 23B, mask 2350 can be usedin steps 2304 and 2306. Mask 2350 comprises metal foil 2352 and an arrayof circles 2354.

In step 2306, material is selectively removed from the composite toexpose a portion of the nanowires. Any method can be used to remove thematerial. For example, the material can be removed using a plasma etchor organic solvent. The amount of material that is removed from thecomposite depends on the particular application for the array. In oneexample, a portion of material is removed from the composite to createan array of wells in the composite that contain exposed nanowires. Forexample, the wells comprising the nanowires can hold an analyte that isanalyzed using the exposed nanowires as sensing elements.

FIG. 24 illustrates an example of a nanowire array 2400. Nanowire array2400 can be formed by mask 2350 shown in FIG. 23B, for example. Material2402 is shown having nanowires 2404 embedded therein. Areas 2408 inwhich material 2402 has been removed are shown. Exposed nanowires 2406are shown. The nanowires 2406 can be processed to allow for efficientdistribution of analyte into the wells or areas 2408 comprising theexposed nanowires 2406. For example, nanowires 2406 can comprisehydrophilic surfaces and material 2402 can comprise hydrophobicsurfaces. It is understood that nanowires 2406 can alternativelycomprise hydrophobic surfaces and material 2402 can comprise hydrophilicsurfaces. It is well known to one of ordinary skill in the art hownanowires can be processed to render their surfaces hydrophobic. Forexample, nanowires can be reacted with an alkylfluorosilane. Arraysprepared in accordance with embodiments of the present invention can beused in a variety of devices. For example, they can be used as sensingelements for the analysis of biological material, including, but notlimited to DNA, RNA, proteins, enzymes, antibodies and the like.

High Capacitance Capacitor Embodiments

In an embodiment, the present invention relates to high capacitancecapacitors including nanowire-material composites, and relates tomethods of producing the same. FIG. 25A shows flowchart 2500 showingexample steps for producing a high capacitance capacitor, according toan embodiment of the present invention. FIG. 25B shows an examplecapacitor 2550, produced according to an embodiment of the presentinvention. Flowchart 2500 begins with step 2502. In step 2502, afreestanding nanowire-material composite having nanowires orientedperpendicular to the composite surface is provided. For example, FIG.25B shows nanowire-material composite 2552, having nanowires 2554oriented perpendicular to the composite surface.

In step 2504, a conducting film is deposited on both surfaces of thefreestanding composite. Any conducting material can be deposited on thecomposite, preferably, the conducting material is a metal. Any method ofdepositing the metal on the composite surface can be used. Examplesinclude, but are not limited to electroless plating and sputtering. Anymetal can be used, preferably, the metal is an inert metal that ishighly conductive and does not react chemically with the composite.Examples of metals include, but are not limited to aluminum, nickel,copper, silver, platinum, and gold. For example, FIG. 25B shows metallayers 2556 a and 2556 b deposited on both surfaces of composite 2552.

In step 2506, an insulator is deposited on one metal surface. Anyinsulator can be used. For example, aluminum oxide can be used. Theinsulator layer can be deposited on the surface using any method knownto one of skill in the relevant art. For example, FIG. 25B showsinsulator layer 2558 deposited on metal layer 2556 a.

In step 2508, a capacitor is assembled. The assembling of a capacitorcan include a variety of steps, including, but not limited to attachingleads to both metal surfaces, rolling-up the films, storing the rolledup films in a canister and sealing the canister. FIG. 25C shows anexample capacitor 2560 having leads 2562 attached to the metal layers2556 a and 2556 b.

FIG. 26 shows flowchart 2600 showing an alternative process forproducing a high capacitance capacitor, according to an embodiment ofthe present invention. In step 2602, a metal foil is provided in whichone surface of the metal foil is coated with an insulator film. Theinsulator film can be made from various insulator materials, including,but not limited to aluminum oxide. In step 2604, gold, or othermaterial, nanoparticles are deposited on a portion of the insulatorfilm. Any method of deposition can be used, for example, the goldnanoparticles can be spin-casted or drop-casted onto a surface of theinsulator film. In step 2606, nanowires are grown on the portioncomprising the gold nanoparticles. In step 2608, a material is depositedon the portion to embed the nanowires and form a nanowire-materialcomposite on the surface of the insulator film. In one embodiment, thematerial comprises a prepolymer or monomer mixture. The material isoptionally further processed in optional further processing steps. Forexample, the material can be hardened. In one example, the materialcomprises a prepolymer and the material is hardened by polymerizing theprepolymer. In step 2610, a metal is deposited on the surface of thecomposite to form a capacitor film. In step 2612, the capacitor isassembled. For example, the capacitor may be assembled by attachingleads to the metal surfaces, rolling the capacitor film, and sealing therolled film in a container.

Flexible Nanocomposite Sheet and Nanofur Embodiments

In an embodiment, the present invention relates to nanowire-materialcomposite films comprising partially exposed nanowires orientedperpendicular to the surface of the composites and relates to methodsfor producing the same. FIG. 27A shows flowchart 2700 showing examplesteps in the preparation of composites comprising partially exposednanowires. In step 2702, a nanowire-material composite film comprisingembedded nanowires oriented perpendicular to the surface is provided.Alternatively, a mixture of nanowires and material is extruded to form asheet of nanowire-material composite. The extrusion process orients thenanowires in the direction of fluid flow. In step 2704, a portion of thematerial is removed to partially expose the embedded nanowires. Anymethod known to one of skill in the relevant art can be used to removethe material, for example, plasma etching or organic solvents are used.FIG. 27B shows examples of the implementation of steps 2702 and 2704.Nanowire-material composite 2750 comprises material 2751 and nanowires2752 embedded in material 2751 and oriented perpendicular to thecomposite surface. After step 2704, material 2751 is partially removedfrom composite 2750. Then, composite 2750 comprises nanowires 2752,wherein a portion 2754 of nanowires 2752 are exposed to produce nanofur.

Nanowire Composite Tube Embodiments

In an embodiment, the present invention relates to nanowire-materialcomposite tubes and processes for producing the same. FIG. 28A showsflowchart 2800 showing exemplary steps in the preparation ofnanowire-material composite tubes. In step 2802, nanowires are contactedwith a material to form a mixture. In step 2804, a mixture comprisingnanowires and material is extruded to form a nanowire-material compositetube. Any method of extrudation known to one of skill in the relevantart can be used. Extrusion can be used to produce materials havingvarious shapes. For example, the mixture can be extruded through acircular die to produce a tubular shape. In another example, the mixturecan be extruded through a linear die to produce a sheet of composite. Inoptional step 2806, material is removed from the one or both of theouter and inner surfaces of the tube to partially expose the embeddednanowires. FIG. 28B shows examples of the implementation of the steps offlowchart 2800. FIG. 28B shows tubular nanowire-material composite 2850comprising material 2854 and nanowires 2852 embedded therein. Tubularcomposite 2858 has a portion of material 2854 removed from the innersurface and comprises partially exposed nanowires 2856 and embeddednanowires 2852.

FIG. 29A shows flowchart 2900 showing an alternative process ofpreparing nanowire-material composite tubes. In step 2902, afreestanding nanowire-material composite film comprising embeddednanowires oriented perpendicular to the surface of the composite isprovided. In optional step 2904, the composite film is cut into stripsof any desired shape or size. In step 2906, the strips are rolled toform tubes and the ends are bonded together. The bonding or attachmentof the ends of the composites can be done using any method known to oneof skill in the relevant art. Exemplary methods include, but are notlimited to, gluing or thermo-welding the ends of the composite. Inoptional step 2908, material is removed from one or both of the outerand inner surfaces of the tube to partially expose the embeddednanowires. FIG. 30 shows a tubular nanowire-material composite 3002,having exposed nanowires 3004 on the interior of the tube.

FIG. 29B shows examples of the implementation of flowchart 2900.Nanowire-material composite 2950 comprises material 2952 and nanowires2954 embedded in material 2952 and oriented perpendicular to the surfaceof the composite. Composite strips 2960 show example implementation ofstep 2904. Rolled and bonded composite strips form tubular composites2970, showing example implementation of step 2906. Bonded area 2972attaches the ends of the composite strip 2960 to form the tubular shape.An example implementation of 2908 is shown by tubular composite 2980.Tubular composite 2980 comprises nanowires 2954 having a portion 2982exposed in the inner portion of tubular composite 2980.

The following examples are illustrative, but not limiting, of the methodand compositions of the present invention. Other suitable modificationsand adaptations of the variety of conditions and parameters encounteredin nanowire-material composite preparation and processing that would beknown to those skilled in the art are within the spirit and scope of theinvention.

EXAMPLES Example 1 Preparation of Nanowire Composite with NanowiresOriented Perpendicular to the Sheet Surface

About 1.0 g of liquid polyethylene glycol diacrylate comprising about 10mg of the photo initiator 2,2-dimethoxy-2-phenylacetophenone was placedin a glass vial. A silicon substrate, measuring about 1×3 cm was coatedwith 40 nm in diameter silicon nanowires. The nanowires were orientedsubstantially perpendicular to the surface of the substrate. Thesubstrate was placed in the glass vial, with about 3 mm of one end ofthe substrate immersed in the liquid mixture. After about 15 minutes,the nanowires had wicked the liquid up to fill the spaces between them.The substrate was removed from the vial and placed under a UV lamp forabout 15 min to polymerize the liquid. A nanocomposite coated substratewas thereby obtained, in which the nanowires were “frozen” at theiroriginal growth orientation.

FIG. 31 is a Scanning Electron Microscope (SEM) image of nanowiresoriented perpendicular to the surface of an example resulting compositematerial, wherein the material comprises poly(ethyleneoxide).

Example 2 Preparation of Nanowire Composite with Nanowires OrientedPerpendicular to the Sheet Surface

About 0.5 g poly(vinylidenefluoride) (PVDF) polymer was contacted withabout 10 g of acetone. After a clear solution formed, about 11.6 mg of40 nm Si nanowires was dispersed into the solution by sonication. About5 g of the dispersion was transferred to a flat bottom glass dish withan inner diameter of about 35 mm. The dish was placed between a pair ofelectrodes and a DC field (about 3000 V/cm, with the negative (−)electrode applied to the top and positive (+) electrode applied to thebottom) was applied and the solvent was evaporated under the field.

Example 3 Preparation of Nanowire Composite with Random NanowireOrientation

About 13 mg of 40 nm Si nanowires was dispersed in about 1 g ofpolyethylene glycol diacrylate. About 10 mg photo initiator of2,2-dimethoxy-2-phenylacetophenone was added. About 5 drops of thedispersion was placed between two glass slides with a gap of about 0.3mm. The glass slide was placed under a UV lamp for 15 minutes topolymerize the polyethylene glycol diacrylate and yield a compositesheet with thickness of about 0.3 nm.

FIG. 32 is a SEM image of an example resulting nanowire-materialcomposite, wherein the nanowires are randomly oriented and the materialcomprises poly(ethyleneoxide).

Example 4 Preparation of Nanowire Composite with Random NanowireOrientation

About 0.5 g PVDF polymer was added to about 10 g acetone. After a clearsolution was formed, about 8.5 mg of 40 nm Si nanowires was dispersedinto the solution by sonication. About 5 g of the dispersion wastransferred to a flat bottom glass dish with an inner diameter of about35 mm. The dish was loosely covered and placed in a hood to allowsolvent evaporation. Upon evaporation of the solvent, a composite sheetwith a thickness of about 0.09 mm was obtained.

FIG. 33 is an SEM image showing an example resulting porousnanowire-material composite, wherein the nanowires are randomly orientedand the material is PVDF polymer. The material was made porous by rapidevaporation of the solvent acetone.

FIG. 34 is an SEM image showing a nanowire-material composite, whereinthe nanowires are randomly oriented and the material is PVDF polymer.The composite is less porous than the composite shown in FIG. 33. Thesolvent was evaporated at a decreased rate, which caused a less porousfilm. This example shows how the porosity of the composite can becontrolled by controlling the rate at which the volatiles (e.g., gasesand fluids) are removed from the nanowire-material composite duringprocessing.

CONCLUSION

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be apparent to persons skilledin the relevant art that various changes in form and detail can be madetherein without departing from the spirit and scope of the invention.Thus, the breadth and scope of the present invention should not belimited by any of the above-described exemplary embodiments, but shouldbe defined only in accordance with the following claims and theirequivalents.

1. A process for depositing oriented nanowires comprising: (a) providinga first substrate having nanowires attached to a portion of at least onesurface, wherein each nanowire has a first end attached to said portion;and (b) depositing a material over said portion to form ananowire-material composite; (c) patterning said nanowire-materialcomposite to form a patterned composite; (d) separating said patternedcomposite from said first substrate; and (e) applying said patternedcomposite to a second substrate such that said nanowires are alignedsubstantially parallel to said second substrate.